The present invention relates to electrical networks which provide power for devices and which may also permit data communications over the network. Typically, these networks include buses which may include both data leads and power leads. In particular, the present invention relates to apparatus for monitoring and indicating a number of different power conditions on the power leads. By way of illustration only, the present invention is disclosed in accordance with the data lead and power lead convention used in the xe2x80x9cDeviceNetxe2x80x9d industrial communications network.
There are various protocols and specifications for networks or buses used for industrial communications. These types of buses are sometimes herein referred to as xe2x80x9cData/Powerxe2x80x9d buses. As indicated and for exemplary purposes only, the present invention is disclosed with reference to a particular industrial communications Data/Power bus protocol known as the xe2x80x9cDeviceNetxe2x80x9d protocol. Persons skilled in the art will understand that the invention has broader application than this particular Data/Power bus, and persons skilled in the art will equally well understand the nature of the invention and how it might be applied to monitor systems other than industrial communication networks which have extended DC power.
The DeviceNet bus system employs five leadsxe2x80x94two power leads, two data leads, and one lead for shielding. By convention or specification, the leads are numbered 1 through 5, with lead 1 being the shield lead, leads 2 and 3 being the power leads (lead 2 is the positive power or voltage lead, and lead 3 is the negative power lead), and leads 4 and 5 being the pair of data leads. Again by convention, when viewing an electrical connector for the bus, the leads are uniformly identified by accepted convention, as will be further described.
Currently, terminator resistors are used to terminate the data leads on DeviceNet systems according to system specifications. The DeviceNet specification requires that the terminating resistor be connected between leads 4 and 5 (the data leads) and that it have a certain value, wattage and tolerance. For example, presently the terminating resistor is at 121 ohm, xc2xc watt, 1% tolerance resistor connected across leads (or connector pins) 4 and 5.
Terminating devices (or xe2x80x9cterminatorsxe2x80x9d for short) are currently manufactured for connecting to male or female connectors of a DeviceNet bus. These terminating devices have the terminating resistor connected between the appropriate connector pins and housed within a molded body formed over an insulating insert which receives and supports the electrical connector elements (whether male or female).
The power used in the DeviceNet bus system is DC power. In order that peripheral devices such as displays or printers or the like, as well as sensors and actuators, can be designed to operate with the DeviceNet system, the voltage on the power leads has a nominal design value, e.g., 24 VDC. In order to determine the voltage actually present in any given system, typically a measuring device such as a volt meter is employed to measure the voltage manually. The technician then makes appropriate decisions as to the existing power conditions and whether they are within system specifications. Manual systems of this type measure only current conditions and do not record incidents when the power may not have met specifications, and therefore, indicated possible maintenance attention. Moreover, such manual systems are dependent on the skill and availability of service personnel.
According to the present invention, a bus terminator includes a circuit having a bi-color light emitting diode (LED) (or two individual indicators) connected in circuit with a current-limiting resistor, if necessary, between pins 2 (V+) and 3 (Vxe2x88x92). The terminator includes a clear or translucent molding material encompassing the LED and current limiting resistor so that the light emitted from the LED may be easily viewed. As used herein, the term xe2x80x9clight-transmissivexe2x80x9d is used to refer to the light transmitting property of the overmold material. It is intended that this term be construed broadly to include not only clear molding material, but also translucent materials of wide range of light transmissivity, provided only that the light can be perceived by an observer in the intended use environment.
By way of example, the LED indicators may have a green and a red color, respectively; and, as is known, the bipolar device consists of two separate LEDs connected together anode-to-cathode so that one LED is lit for one polarity and the other LED is energized if the applied voltage is of reverse polarity.
In this manner, using the terminator of the present invention, a person viewing the terminator can readily determine whether: (i) there is no power present (i.e., no light being emitted from the LED); (ii) power is present with the correct polarity (green light being emitted from the LED); or (iii) power is present but of a reverse polarity (red light being emitted from the LED).
In this manner, the observer can determine readily, without the need of instruments, whether power is present, and if so, whether it is of the correct or reversed polarity.
Moreover, as will be further disclosed below, by sensing the voltage at the two power leads and transmitting the sensed voltage to a microprocessor, the microprocessor, installed within a network terminator or a Tee, together with a plurality of LEDs (each of a different color), may detect and signal a wide range of present and past power conditions. By way of example, which is not intended to limit the invention in any manner, a steady green light may mean that the voltage is within a normal range and of proper polarity and no errors have been detected since the last reset. A steady red light may indicate an unacceptably high voltage or xe2x80x9covervoltage.xe2x80x9d A steady blue light may indicate a low voltage or xe2x80x9cundervoltage,xe2x80x9d whereby the voltage is beneath the normal desired voltage range. A flickering (or other flash sequence) red light generated by the microprocessor may indicate that there is a voltage surge, that is, an overvoltage condition followed by return to normal voltage. A flickering blue light may indicate an undervoltage followed by a return to normal, or xe2x80x9cbrownout.xe2x80x9d Similarly, a steady amber light may indicate a detected voltage xe2x80x9cripple,xe2x80x9d and a flickering amber light may indicate a xe2x80x9cglitchxe2x80x9d (or xe2x80x9ctransientxe2x80x9d) in which the ripple condition occurred but no longer persists. The conditions indicated by a flickering indicator are latched, thus preserving, at least temporarily and until reset, a record of the indicated event for later viewing. The conditions and events mentioned may vary and the limits or thresholds may be modified according to the designer""s choices. Unless otherwise specified herein, all voltages referred to are DC voltages.
The microprocessor and indicating LEDs may be incorporated into a terminating device in the case where data leads are included in a network bus being monitored. In this case, the indicating LEDs are encased in a light transmissive molded material. Alternatively, the electronics and LEDs may be incorporated into a Tee configuration which may be inserted into the network at an intermediate monitoring location or at a junction point. The Tee configuration includes a panel of light transmissive overmold for permitting viewing of the indicators.
Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed description of exemplary embodiments accompanied by the accompanying drawings wherein identical reference numerals will refer to like parts in the various views.